1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus such as a digital copying machine which includes a memory means, e.g., a page memory.
2. Description of the Related Art
As an apparatus of this type, an image forming apparatus such as a color digital copying machine is widely known. In such an image forming apparatus, an optical system is moved to illuminate an original, and the reflected light from the original is read by a photoelectric conversion device such as a CCD and output after being subjected to various image processing operations.
Generally, an image forming apparatus of this type includes an image transfer member such as a transfer drum, and color-separated images of magenta, cyan, yellow, and black are sequentially overlapped on this transfer member to form a color image.
As recording paper cassettes for storing sheets of recording paper for printing out color images formed, A3-, A4-, B4-, and B5-size cassettes for example, are prepared in correspondence with the sizes of recording paper. In copying an A3-size original by reducing it to an A4 copy size, an A4R-size recording paper cassette which is the lateral form of A4-size recording paper is also required. Likewise, a B5R-size recording paper cassette is necessary when a B4-size original is to be copied by reducing to a B5 copy size.
It is also a common approach to temporarily store read image signals into a page memory and form images while reading out the images stored in the memory.
Unfortunately, the above conventional apparatuses have the following problems.
That is, the access time of, e.g., a DRAM used as the page memory has its limit, and this restricts the rate of read and write of image signals. Therefore, the image formation speed cannot be raised in forming images by reading out image signals from the memory. In addition, if the number of recording paper cassettes is increased to meet various sizes of recording paper for use in printing out images, a paper feed mechanism is complicated and increased in size. This unavoidably increases the size of an apparatus.
Furthermore, image signals to be stored in the memory include those in which one pixel is converted into a multivalued signal and those in which one pixel is converted into a binary signal. The conventional apparatuses discussed above are not so designed as to reduce the image forming time when the memory is used or store both the multivalued and binary signals in the memory with a high efficiency.
It is an object of the present invention to solve the above conventional problems.
It is another object of the present invention to provide an image forming apparatus capable of processing both binary and multivalued image signals at a high efficiency.
To achieve the above object, according to one aspect of the present invention, there is provided an image forming apparatus, comprising input means for selectively inputting a binary image signal and a multivalued image signal for one pixel from an external device, holding means for holding the input image signal for a predetermined period and outputting the image signal in units of a plurality of pixels, the holding means holding the image signal for a period corresponding to the number of the unit pixels and an information amount per pixel, and changing the number of the unit pixels in accordance with whether the input image signal is a multivalued signal or a binary signal for one pixel, storage means for storing the image signal from the holding means in units of the plurality of pixels, readout means for reading out the image signal from the storage means in units of the plurality of pixels, and image forming means for forming an image on the basis of the image signal read out by the readout means.
It is still another object of the present invention to provide an image forming apparatus capable of increasing the image formation speed in forming images corresponding to binary and multivalued image signals, by performing optimum processing for each image.
To achieve the above object, according to another aspect of the present invention, there is provided an image forming apparatus, comprising input means for selectively inputting a binary image signal and a multivalued image signal for one pixel from an external device, storage means for storing the image signal, memory control means for controlling write/read access of the image signal to the storage means, the memory control means performing the write/read access of the image signal to the storage means in units of a plurality of pixels, and changing the number of the unit pixels in accordance with whether the image signal to be processed is a binary image signal or a multivalued image signal, and image forming means for forming an image corresponding to the image signal from the storage means.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.